Now we see through a glass, darkly...
- Apr 5, 2016
1) He's saying the opposite. The ability to back and crop will give him a different image. That's why he is considering such a camera.
2) He's right. Its elemental optical knowledge. As you move away from the subject (using the same lens) more of the subject moves into the focus plane. With enough pixels you can afterwards crop in to get the magnification you need. I do not do macro myself, but can see how this could be an advantage as much macro work has a very shallow focal plane to work with. Try imagining a gigapixel camera with a hypothetical lens to match. You take a garden shot - and afterwards you could crop down to a bee sitting on one of the flowers. And all of the bee would in perfect focus.
Except when you crop you increase the magnification ratio (from image size on the sensor to image at a particular display size) which decreases depth-of-field. It's just like increasing the display size of the exact same image decreases the depth-of-field when viewed from the same distance. Anytime you increase magnification, some blur that looked in focus before will become perceivable as blur.